Deformable non-cellular polyurethane polishing wheel

Abstract

A non-cellular polyurethane polishing and finishing wheel is disclosed having a molded annular matrix reinforced at the inner circumference by a circumferential reinforcing means. The radially outer portion of the matrix is free to deform during use and is formed of a flexible elastomeric polyurethane having a no-grain Shore A durometer hardness from about 30 to about 55 and a high tensile strength. Proper distribution of the abrasive refractory grains is achieved by employing a polyurethane prepolymer having a high viscosity of 2000 to 6000 centipoises at the curing temperature, and the curing agent is selected to provide the required flexibility and tensile strength and also to effect curing rapidly so that the abrasive grains remain in position during curing. The polyurethane composition preferably contains up to 100 parts of finely divided abrasive material, 3 to 20 parts of mica, and up to 10 parts of molybdenum disulfide per 100 parts by weight of the polyurethane prepolymer. The polyurethane polishing and finishing wheels of the present invention have a useful life at least several times that of the flexible wheels previously used and make it commercially practical for the first time to employ such wheels on machines such as O.D. grinders, centerless grinding machines and the like.

Having described my invention, I claim: 
     
       1. A flexible reinforced polyurethane finishing wheel for a centerless grinder comprising a dense molded non-cellular annular matrix with a diameter of at least 10 inches and an axial width of at least one inch having a circumferential reinforcing means which resists radial expansion of said matrix, the radially outer portion of said matrix being deformable and being formed of a cured solid elastomeric polyurethane composition having a no-grain Shore A durometer hardness from about 30 to about 55, a density of at least 100 pounds per cubic foot, and a tensile strength of at least 4000 pounds per square inch and being capable of being elongated several hundred percent, said elastomeric composition comprising essentially a solid linear polyurethane which is the reaction product of a long-chain polyol having terminal hydroxyl groups and a molecular weight of at least 500 and an organic polyisocyanate having 2 to 3 functional isocyanate groups, said composition containing, per 100 parts by weight of said polyurethane, a minor amount no less than 50 parts by weight of finely divided abrasive refractory grains. 
     
     
       2. A flexible reinforced polyurethane finishing wheel for a centerless grinder comprising a flat flexible non-cellular annular matrix with a cylindrical work-engaging surface having a diameter of at least 10 inches and an axial width of at least one inch molded from a solid elastomeric composition and having a circumferential reinforcing means which resists radial expansion of said matrix, said reinforcing means terminating within two inches of the circumferential work-engaging surface of the wheel, said molded elastomeric composition having a no-grain Shore A durometer hardness from about 30 to about 55, a density of at least 100 pounds per cubic foot, and a tensile strength of at least 4000 pounds per square inch and being capable of being elongated several hundred percent, said elastomeric composition comprising essentially a solid linear polyurethane which is the reaction product of a long-chain polyol having terminal hydroxyl groups and a molecular weight of at least 500 and an organic polyisocyanate having 2 to 3 functional isocyanate groups, said composition containing, per 100 parts by weight of said polyurethane, a minor amount no less than 50 parts by weight of abrasive refractory grains having a practicle size from about 80 to about 320 grit. 
     
     
       3. A flexible polyurethane finishing wheel according to claim 2 in which said composition in the uncured state comprises a polyester or polyether urethane prepolymer having a viscosity at 212° F. of from 1500 to 6000 centipoises, from 0.4 to 10 parts of molybdenum disulfide per 100 parts by weight of said polyurethane, and a curing agent which cures and stiffens the polyurethane composition within 2 minutes after it is placed in the heated mold and before the abrasive grains can settle. 
     
     
       4. A process of making a finishing wheel comprising mixing 100 parts by weight of a polyester or polyether urethane prepolymer having a viscosity at 212° F. from about 1500 to about 6000 centipoises with from about 40 to about 90 parts by weight of abrasive refractory grains and a curing agent to provide a fast-curing polyurethane composition with the abrasive grains evenly distributed therein, causing the resulting composition to flow into a mold cavity containing a circumferential reinforcing member, and heating the mold to a temperature of at least 200° F. to cure and stiffen the polyurethane composition within two minutes after it is introduced into the mold cavity and before the abrasive grains can settle, and continuing the curing to provide a cured non-cellular polyurethane with a tensile strength of at least 4000 pounds per square inch capable of being elongated at least 300 percent, said curing agent being selected to provide such tensile strength and such fast curing and to provide a cured grinding wheel with a no-grain Shore A durometer hardness from about 30 to about 60 and a density of at least 100 pounds per cubic foot, a pressure in excess of one hundred pounds per square inch being applied during curing, said abrasive grains and said prepolymer being heated to a temperature of at least 200° F. before they are mixed together, said mold and said reinforcing member being heated to a temperature of at least 200° F. before the polyurethane composition is caused to enter the mold cavity. 
     
     
       5. A finishing wheel according to claim 1 wherein said composition contains from about 0.4 to about 10 parts of molybdenum disulfide per 100 parts by weight of said polyurethane. 
     
     
       6. A finishing wheel according to claim 1 wherein said composition in the uncured state comprises a polyester or polyether urethane prepolymer having a viscosity at 212° F. of from 1500 to 6000 centipoises.